Busemann Biplane
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The Busemann biplane is a theoretical
aircraft An aircraft is a vehicle that is able to fly by gaining support from the air. It counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines ...
configuration invented by Adolf Busemann, which avoids the formation of N-type
shock wave In physics, a shock wave (also spelled shockwave), or shock, is a type of propagating disturbance that moves faster than the local speed of sound in the medium. Like an ordinary wave, a shock wave carries energy and can propagate through a me ...
s and thus does not create a
sonic boom A sonic boom is a sound associated with shock waves created when an object travels through the air faster than the speed of sound. Sonic booms generate enormous amounts of sound energy, sounding similar to an explosion or a thunderclap to ...
or the associated
wave drag In physics, mathematics, and related fields, a wave is a propagating dynamic disturbance (change from equilibrium) of one or more quantities. Waves can be periodic, in which case those quantities oscillate repeatedly about an equilibrium (r ...
. However in its original form it does not generate
lift Lift or LIFT may refer to: Physical devices * Elevator, or lift, a device used for raising and lowering people or goods ** Paternoster lift, a type of lift using a continuous chain of cars which do not stop ** Patient lift, or Hoyer lift, mobil ...
either. A Busemann biplane concept, which provides adequate lift, and which can reduce the wave intensity and drag but not eliminate them, has been studied for a "boomless" supersonic transport.


Origins

Busemann's original biplane consists of two triangular cross-section plates a certain distance apart, with the flat sides parallel to the fluid flow. The spacing between the plates is sufficiently large that the flow does not choke and supersonic flow is maintained between them. Supersonic flow around a conventional wing generates compressive sonic shock waves at the leading and trailing edges, with an expansion wave in between them. These shock waves correspond to pressure changes which impede airflow, known as
wave drag In physics, mathematics, and related fields, a wave is a propagating dynamic disturbance (change from equilibrium) of one or more quantities. Waves can be periodic, in which case those quantities oscillate repeatedly about an equilibrium (r ...
. In the Busemann biplane, the forward high pressure shock wave is created internally and reflects symmetrically between double-wedge inner surfaces. These interfere to cancel out both themselves and the following shock waves, leaving no external wave to propagate to infinity and hence avoiding wave drag. The flat upper and lower surfaces generate no shock waves because the flow is parallel. The internal alignment of the shock waves means that Busemann's biplane produces minimum
wave drag In physics, mathematics, and related fields, a wave is a propagating dynamic disturbance (change from equilibrium) of one or more quantities. Waves can be periodic, in which case those quantities oscillate repeatedly about an equilibrium (r ...
. However, the flat external surfaces and internal symmetry also mean that Busemann's design does not produce any lift at the design point for optimal shock and drag reduction.


Off-design conditions

Operation away from the design cruise speed or angle of attack destroys the constructive interference and results in shock choking and flow hysteresis effects, which greatly increase drag. In shock choking, the shockwaves reduce their backwards angle with each reflection off the tapered wing surfaces until they form a shock wall across the gap. This causes a buildup of pressure and slowdown of flow speed, so that flow hysteresis occurs, in which the slowing of the air causes the choking to persist through and beyond the design point before it clears at a higher aircraft speed.Ma, Wang, Wu and Ye. (2020)
"Avoiding Choked Flow and Flow Hysteresis of Busemann Biplane by Stagger Approach"
''Journal of Aircraft'', Volume 57, Number 3, May 2020.


Lifting Busemann biplanes

According to
Newton's laws of motion Newton's laws of motion are three basic laws of classical mechanics that describe the relationship between the motion of an object and the forces acting on it. These laws can be paraphrased as follows: # A body remains at rest, or in moti ...
, in order to obtain upward lift on the wings, in reaction the air passing over them must be deflected downwards. At supersonic speeds this creates at least one shock wave and possibly more. Like any other airfoil, the Busemann biplane can be given a small positive angle of attack to generate lift in this way, however it will also now generate external shockwaves. The Busemann biplane configuration can still be used to minimize the energy of these shock waves and the associated drag.Kusunose, Matsushima and Maruyama. (2011)
"Supersonic biplane — A review"
''Progress in Aerospace Sciences'' 47. pp.53–87.
Wu, Jameson and Wang. (2012)
"Adjoint based aerodynamic optimization of supersonic biplane airfoils"
''Journal of Aircraft'', Vol.49, No.3. May–June 2012. pp.802 ff.
Wave drag has two causes, one due to the bulk or form of the plane and the other due to the lift generated. The Busemann concept can eliminate form shock drag but not that due to lift. Busemann's original geometry eliminated all wave drag and hence also lift. Modern Busemann type designs can create lift, with its associated shockwave, while still eliminating much or all of the form drag, thus achieving considerable improvements in efficiency over conventional designs. They can also allow adequate performance over a range of speeds and angles of attack. The problems of off-design choking and hysteresis can be resolved by the use of variable-geometry devices, such as flaps and slats which may also serve as high-lift devices during takeoff and landing. Another approach is to modify the airfoil geometry to provide acceptable performance over a range of off-design conditions, at the expense of some form drag even at the optimum design point. The Busemann biplane concept has been studied as a concept for a "boomless" supersonic transport.


See also

*
Pratt & Whitney J58 The Pratt & Whitney J58 (company designation JT11D-20) is an American jet engine that powered the Lockheed A-12, and subsequently the YF-12 and the SR-71 aircraft. It was an afterburning turbojet engine with a unique compressor bleed to the a ...
used a mixed compression inlet, a configuration sensitive to unstarts, ie shock expulsion giving an external bow shock-wave. *
Catamaran A Formula 16 beachable catamaran Powered catamaran passenger ferry at Salem, Massachusetts, United States A catamaran () (informally, a "cat") is a multi-hulled watercraft featuring two parallel hulls of equal size. It is a geometry-stab ...
boats with reduced wave-making resistance due to their so-called split hull configuration.


References

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External links


Busemann's Biplane - Explanation and Theory
Biplanes Aerodynamics Wing configurations Aircraft wing design